Discovering how flow fields hinder bubble removal from porous transport layers through pore scale modelling

We show how the presence of the PTL/flow field interface inhibits gas bubble removal and leads to higher PTL gas bubble saturations, which is particularly relevant to a broad range of electrolyzers, from hydrogen production to CO 2 reduction. The land regions of a flow field delay the onset of breakthrough, significantly extending gas bubble cluster propagation within the PTL. As a results, we observe a bulk gas saturation of 0.574 with flow fields compared to 0.438 without flow fields (31.1 % higher). Further, due to severe bubble accumulation in the land regions of the PTL with flow fields, gas saturation is 0.661 under the lands compared to 0.458 under the channels (44.3 % higher). Heterogeneities in gas saturation distributions in the PTL with flow fields increase over time due to the delayed onset of breakthrough for bubble clusters accumulating in the land regions, and this accumulation inhibits water reactant delivery to the catalyst layer. While in practice it may be difficult to eliminate flow fields in the electrolyzer, our work illustrates the critical importance of designing flow fields that will minimize the obstruction of reactant water delivery to the catalyst layer due to the tendency for bubbles to accumulate under the lands.